Preparation of high test calcium hypochlorite

ABSTRACT

Calcium hypochlorite compositions, suitable for bleaching and sanitation uses, are provided which have lowered rates of propagation of decomposition when heated. These novel compositions contain 75 to 82 percent of calcium hypochlorite and 6 to 12 percent of water, balance usual diluents of calcium hypochlorite including calcium chloride, carbonate, hydroxide and sodium chloride.

United States Patent Faust 51 June 13, 1972 [54] PREPARATION OF HIGHTEST CALCIUM HYPOCHLORITE [72] Inventor:

[73} Assignee: Olin Corporation [22] Filed: Sept. 2, I970 [2l] Appl.No.: 69,130

John P. Faust, Hamden, Conn.

[52] US. Cl ..252/l87, 23/86, 252/99 {51] Int.Cl.

[58] Field of Search ..252/l87, 99, 94; 23/86, 152

[56] References Cited UNITED STATES PATENTS 3,544,267 12/1970 Dychdala.23/86 3,584,996 6/l97l Hughes ..252/l87 Primary Examiner-Leon D. RosdolAssistant Examiner-lrwin Gluck Attorney-Gordon D. Byrkit, Donald F.Clements, Thomas P. ODay, F. A. lskander and Eugene Zagarella, Jr.

[ ABSTRACT 3 Claims, No Drawings PREPARATION OF HIGH TEST CALCIUMHYPOCHLORITE This invention relates to novel calcium hypochloritecompositions and the method of making them. In one aspect, the inventionrelates to solid compositions containing 75 to 82 percent of calciumhypochlorite and 6 to 12 percent of water. Other diluents normallypresent in solid calcium hypochlorite are also suitably present in thecalcium hypochlorite compositions. These novel compositions are designedand have the advantage, over calcium hypochlorite compositionspreviously known to the art, of having a substantially slower rate ofdecomposition when accidentally contacted by organic or other readilyoxidizable materials or by heat or fire.

Calcium hypochlorite is a well known dry chemical and it has been madeand sold commercially for many years. It is used as a source of drychlorine for sanitation purposes, for example, in disinfecting the waterof swimming pools. The maintenance of a small residual of availablechlorine suitably from about 0.5 to 1 part per million parts of water issufficient to insure prompt destruction of bacterial contamination, sothat the water is safe to swim in.

With widespread installation of swimming pools and resulting expansionof sales of calcium hypochlorite to the general public rather thanprimarily to other chemical manufacturers, municipal and other largescale users, this vigorously reactive chemical has been placed in thehands of many who are unskilled in its use and unfamiliar with thehazards possibly resulting should it be involved in a fire. As a result,frequently of ignorance or carelessness, fires involving calciumhypochlorite have occurred which endangered life and property. it isessential to provide a calcium hypochlorite product having a reducedrate of decomposition even when misused or carelessly handled but whichstill retains high test and effectiveness sufficient for sanitationpurposes.

In a number of instances, serious fires have resulted when a solidhypochlorite has been contacted by a lighted cigarette. While droppingof a lighted cigarette into a commercial preparation of calciumhypochlorite is not a common occurrence, it does happen. Probably foreach million of 100 pound drums of calcium hypochlorite sold, one willhave a lighted cigarette dropped in it; it is unlikely that theprobability will be greater than one for each half million drums sold.The directions given with the product always warn against such apossibility and against other forms of contamination. To avoid thishazard, attempts have been made to safen calcium hypochlorite,especially against the hazard of contact with a lighted cigarette.

Various diluents have been proposed for use with solid hypochlorite forvarious purposes, including stabilization (e.g., Na,0, in U.S. Pat. No.1,961,576), detergent effects (e.g., U.S. Pat. Nos. 2,320,27980),sequestering calcium (e.g., U.S. Pat. Nos. 2,l66,362-3; 2,959,554) andfor other purposes. However, because of the chemical reactivity of thehypochlorites, the choice of diluents is severely limited. Many proposeddiluents deleteriously affect the stability of hypochlorites and causethem to lose available chlorine rapidly. Especially at elevatedtemperatures, many proposed diluents cause rapid decomposition incontact with hypochlorites.

in the early commercialization of calcium hypochlorite, calciumhydroxide was a common diluent. Many of the processes employed for thepreparation of calcium hypochlorite tended to leave calcium hydroxide inthe product. Another common diluent was sodium chloride, a naturallyformed diluent in the processes used by the Mathieson Alkali Works,Inc., who introduced HTH" brand of calcium hypochlorite in I928.

The first products put out were advertised to contain 65 percent calciumhypochlorite. However, because buyers have a natural reluctance to payfor diluents, the product was raised to contain 70 percent or more ofcalcium hypochlorite. Purchasers continued to press for higher tests andby I935 the Mathieson Alkali Works was shipping carload lots of productcontaining 80 percent of more ofcalcium hypochlorite.

When several drums of HT H containing over percent of calciumhypochlorite became involved in tires, shipments of 80 percent andhigher material were discontinued and commercial production of calciumhypochlorite has remained at about 70 percent of over 30 years.

Further work to safen calcium hypochlorite compositions has led to aprocess in which most of the sodium chloride formed in the manufacturingprocess is removed prior to drying the calcium hypochlorite product andis replaced by sodium nitrate prior to drying. Later, higher testcalcium hypochlorite preparations (80 to percent available chlorine)were made by known methods and these were diluted to 72 to 74 percentcalcium hypochlorite content by addition of crystalline sodium nitrate.ln a still more recent development, described in U.S. Pat. No.3,560,396, calcium hypochlorite is advantageously diluted withspray-formed sodium nitrate.

In another recent development, described in German Offenlegungschrift1,944,097, a measured amount of water is uniformly added to anessentially dry, dust-containing commercial calcium hypochloriteproduct, until the water content reaches about 4 to l5 percent. Thecalcium hypochlorite preparation thus produced is a free-flowinggranulate which is less susceptible to decomposition, free from dust andhas a particle size of about 0.075 to 2 mm. The water addition producesan exothermic reaction and the temperature of the mixture is kept below66 C. by cooling. A preferred method of water addition is by sprayingthe stirred mass. The resulting product contains 4 to 15 percent ofwater and, starting with a commercial 70 percent calcium hypochloritematerial, the final product contains from 59 to 67 percent calciumhypochlorite. It is considerably "safened with respect to i gnition andexothermic decomposition.

One object of this invention is to provide high test calciumhypochlorite compositions which are safened with respect todecomposition rates but without addition of inorganic salt diluent.

Another object of the present invention is to provide compositionshaving materially lowered rates of propagation of decomposition whilemaintaining high available chlorine content compared with anycompositions of the prior art.

Another object of the present invention is to provide an improved methodof preparing the safened compositions of this invention.

Other objects of this invention appear elsewhere in this specification.

ln one aspect, the present invention provides calcium hypochloritecompositions containing 75 to 82 percent of Ca(OCl),, 6 to 12 percent ofwater, balance minor amounts of constituents normally present in calciumhypochlorite preparations.

The starting material for the purposes of the present invention is asolid, dry calcium hypochlorite composition containing 85 to percent ofcalcium hypochlorite and under 5 percent of water, balance inertmaterials usually associated therewith resulting from the process ofmanufacture, e.g., sodium chloride, calcium hydroxide, chloride andcarbonate. In a heretofore customary practice of calcium hypochloritemanufacture, the calcium hypochlorite is obtained as a slurry containingcrystals of calcium hypochlorite dihydrate [Ca(OCl), 21,01 in a motherliquor consisting essentially of an aqueous solution of calciumhypochlorite and sodium chloride. The slurry is filtered on a rotaryvacuum filter to produce a cake that retains sufficient mother liquor tohave a moisture content of 45 percent to 50 percent by weight. The wetcake, e.g., from an Eimco filter, when dried directly yields the calciumhypochlorite of commerce. However, when such a wet cake is furtherprocessed, e.g., by filtration, centrifuging or otherwise to separatefurther quantities of liquor, a wet solid is obtained which on dryingproduces the 85 to 90 per' cent calcium hypochlorite used as a startingmaterial according to this invention.

in the process of this invention a calcium hypochlorite containing 85 to90 percent calcium hypochlorite is exposed to an inert gas, e.g., air ornitrogen, having a humidity of 80 to 100 percent at temperatures of 80to l F. for a time sufficient to form a hypochlorite product containing6 to 12 percent water. The granular (0.05 to 3 mm.) calcium hypochloriteproduct contains from 75 to about 82 percent calcium hypochlorite. it isnot only safened with respect to ignition and exothennic decompositionbut also is marketable as a guaranteed 70 percent calcium hypochloritehaving a suitable margin for loss during shelf storage.

EXAMPLE I A sample of Eimco filter cake containing 39.42 percent calciumhypochlorite and 48.8 percent water was taken from an operationproducing commercial 70 percent calcium hypochlorite. It was furtherpressed in a porous bag to reduce the water content and then dried in avacuum oven. The resulting dried material contained 86 percent calciumhypochlorite and 1 percent water. The dried material was exposed to airat 100 F. having 90 percent relative humidity for l hour. It thencontained 76.24 percent calcium hypochlorite and l 1.28 percent water.When a lighted cigarette was laid on the product, it produced noself-sustaining reaction although the 86 percent material reactedvigorously in a self-sustaining reaction until all of that product wasdecomposed.

EXAMPLE]! Calcium hypochlorite filter cake from a commercial operationfor preparing '70 percent calcium hypochlorite and containing about 25percent water was vacuum dried to 4.65 percent water and 85.3 percentcalcium hypochlorite. This starting material was reactive toward lightedcigarettes and burning matches.

Part of the above-described starting material was placed in adesiccator, the bottom of which contained water at l04' F. Thedesiccator was flushed thoroughly with nitrogen to remove all the air.The product remained in the atmosphere of wet nitrogen for 20 minutes. Aportion was removed and found to be unreactive toward lighted cigarettesand matches. The product was found to contain 82 percent calciumhypochlorite and 9.3 percent water.

EXAMPLE [I] Another portion of the starting material described inExample I! was exposed to air at 100 F. having 90 percent relativehumidity for 10 minutes. A sample was found to be unreactive towardlighted cigarettes and matches. it contained 10.4 percent watcr and80.85 percent calcium hypochlorite.

What is claimed is:

1. Method of preparing a granular calcium hypochlorite compositioncontaining 75 to 82 percent of calcium hypochlorite, 6 to 12 percent ofwater, balance sodium chloride and minor amounts of constituentsnormally present in calcium hypochlorite by exposing granular calciumhypochlorite containing 85 to percent calcium hypochlorite to a gasselected from the group consisting of air and nitrogen and having ahumidity of 80 to percent at temperatures from 80 to F. for a timesufficient to produce a calcium hypochlorite product containing from 6to 12 percent of water and from 75 to 82 percent of calciumhypochlorite.

2. Method as claimed in claim 1 in which said inert gas is air.

3. Method as claimed in claim 1 in which said inert gas is nitrogen.

I! I! i i

2. Method as claimed in claim 1 in which said inert gas is air. 3.Method as claimed in claim 1 in which said inert gas is nitrogen.